The use of sensors for remote monitoring is ubiquitous because it facilitates the monitoring of industrial or environmental conditions that would otherwise be economically unfeasible to monitor. Examples include the monitoring of manufacturing plants, monitoring soil moisture in agriculture, or monitoring pipelines for leaks. The current invention will be presented in the context of pipeline monitoring but those skilled in the art will recognize that it can be applied to numerous types of sensor monitoring applications.
Pipelines are widely used for transporting commodities such as water, natural gas, or petroleum products. Leakage from a pipeline can result in significant economic losses or environmental damage and, therefore, there is a great interest in mitigating any such damages from pipeline operations. Assurances from pipeline companies regarding the adequate monitoring of a proposed pipeline may also be a major factor in determining whether or not a pipeline can be built.
Although there are existing methods for pipeline monitoring, they are often not adopted in industry because of their excessive cost, low reliability, or poor accuracy. An overview of some existing methods follows.
U.S. Pat. No. 4,029,889 (Mizuochi) uses a coaxial cable where the outer jacket is water-resistant but is either permeable to petroleum or dissolved by petroleum. When the petroleum permeates the insulation between the shield and the center conductor, there is a local change in the electrostatic capacity. This change can be detected by transmitting a pulse down the cable and monitoring the reflected waveform.
U.S. Pat. No. 4,206,402 (Ishido) also utilizes a coaxial cable, but in this case the cable is segmented and individual segments are monitored for changes in its electrical properties.
U.S. Pat. No. 4,336,708 (Hobgood et al.) uses a temperature-based system for localizing leaks. However, this system is for localizing leaks in a section of pipe where a leak is known to exist. It is not a monitoring system for the detection of leaks.
There are several methods in the prior art that use acoustic means, U.S. Pat. No. 4,457,163 (Jackle) monitors the acoustic emissions along a pipeline to detect and localize leaks. In U.S. Pat. No. 4,996,879 (Kruka, et al.) sonic energy is introduced into an underwater pipeline and an array of hydrophones is used to localize the leak. U.S. Pat. No. 5,117,676 (Chang) uses a plurality of microphones to monitor a natural gas pipeline where the expected characteristic frequency of the emissions can be determined from the pipeline characteristics. In U.S. Pat. No. 5,361,636 (Farstad et al.) acoustic means are used to determine the rate of leakage through a valve within the pipeline. In this case, the leaked contents are contained within the pipeline system. In U.S. Pat. No. 5,974,862 (Lander, et al.), signals from a plurality of acoustic sensors are digitized and transmitted to a system where their signals can be analyzed using cross-correlation.
In U.S. Pat. No. 7,564,540 (Paulson), two fiber-optic based measurements are used. The first uses an interferometer to detect and classify anomalies in the received optical signal. The second measurement uses time-domain reflectrometry or Brillouin scattering to localize the detected anomaly.
In U.S. Pat. No. 7,591,285 (Wittmann), which is for aboveground pipelines, fluid that escapes from the pipe is collected by a catchment system and pooled at the location of the sensor element.